For nearly 20 years it has been inconveniencing our springs and summers by prowling around us to sting us. He is the Aedes albopictus, better known as the tiger mosquito. Spotted for the first time in France in 2004 in Menton after having meticulously colonized Italy from south to north, the small black and white striped flying insect continues its inexorable expansion by going up towards the north of the country. Only a small third of the departments are currently spared by the presence of this pest, originating in Southeast Asia.
“Under the effect of heat, the larvae will hatch after 6 days instead of 8”, Didier Fontenille, medical entomologist
If the tiger mosquito has taken over the world thanks to trade flows and tourism, does climate change play a role in its proliferation? “It is, in fact, one of the components”explains Didier Fontenille, research director of the Institute of Research for Development (IRD) and medical entomologist specializing in vector-borne diseases (transmitted, in particular, by insects).
In question, the rise in temperatures which creates, in particular, climates more conducive to the rapid reproduction of the biting insect. “Under the effect of heat, the larvae will hatch after 6 days instead of 8, which will multiply the number of generations of tiger mosquitoes in the year. Favorable temperatures can also prolong their lifespan”details the specialist.
And that’s not the only bad news. Zika virus, dengue fever, chikungunya… Aedes albopictus is also a vector of tropical diseases that it can transmit to humans via the anticoagulant saliva that females inoculate into our bodies when they bite. A contamination that can only take place if the mosquito is itself at the end of its incubation, “period during which the virus multiplies in his body and moves there to gradually reach his salivary glands”explains Didier Fontenille.
If this incubation time can range from 4 to 8 days depending on the virus, the heat will also have the effect of reducing this period, specifies the medical entomologist. But the effects of the heat don’t stop here…
When the heat wave threatens the tiger mosquitoes
A bit like humans, if it appreciates the heat, the small striated insect nevertheless suffers, too, when the climate becomes too extreme. “What the tiger mosquito prefers are temperatures between 25 and 30°C. If it can survive cool temperatures thanks to extraordinary adaptive capacities, its life expectancy will decrease beyond 35°Cnuance Didier Fontenille. During a heat wave, experiments carried out in the laboratory show that it easily drops by 30 to 20 days. Above 50°C, it dies. Same thing at 5°C.
But the specialist nevertheless qualifies: “temperature, hygrometry… all these climatic components, as we can see, affect our models but only for a part. The main reason for the proliferation of the tiger mosquito remains human behavior”he warns.
Because if the Aedes albopictus proliferates so much, it is above all because of the small stagnant water reservoirs that we leave to grow near our homes and which act as ideal nurseries for the larvae (saucer under the flower pots, plants, buckets or toys, uncovered water collectors, watering can, etc.).